LeetCode 36: Valid Sudoku | CSharp Solution | Hash Sets & Matrix Traversal

🧩 In this video, I solve the #leetcode Valid Sudoku problem, determining if a partially filled 9x9 Sudoku board is valid according to standard rules. We'll use #hashsets and efficient #matrix traversal techniques to check row, column, and 3x3 subgrid constraints. ⏱️ **Complexity Analysis:** - Time Complexity: O(1) - We always check exactly 81 cells with constant time operations - Space Complexity: O(1) - We store at most 27 hash sets of limited size ## 📌 Timestamps 00:00 - Understanding problem statement 00:47 - Whiteboarding 02:10 - Dry-run 04:10 - Big O Notation explained 05:07 - C# code walk-through 06:28 - Solution analysis - runtime + memory ## 🔑 Key Concepts - Hash set usage for duplicate detection - Matrix traversal techniques - Validation algorithms - CSharp HashSet implementation - Array indexing and manipulation ## 📚 Learning Highlights - How to efficiently validate constraints in a grid - Techniques for checking multiple conditions simultaneously - Optimizing validation loops in CSharp - Converting 2D position to subgrid index efficiently ## 🔄 Related Problems - LeetCode 37: Sudoku Solver - LeetCode 73: Set Matrix Zeroes - LeetCode 54: Spiral Matrix - LeetCode 79: Word Search ## 👥 Target Audience This video is perfect for software engineers preparing for technical interviews, CSharp developers looking to improve their problem-solving skills, and anyone interested in algorithm implementation. ## 📋 Prerequisites - Basic understanding of CSharp syntax - Familiarity with arrays and collections - Understanding of hash sets and their operations ## 🔗 Important Links - LeetCode problem: https://leetcode.com/problems/valid-sudoku/ - Solution code: https://leetcode.com/problems/valid-sudoku/solutions/6972791/sudoku-validation-solution-in-c-with-vid-nlhk ## 💡 Additional Tips - Remember to check for duplicates in rows, columns, and 3x3 subgrids separately - Use integer division to map cell positions to their respective 3x3 subgrid - Consider validating as you iterate to exit early on invalid inputs If you found this solution helpful, please hit that like button and subscribe for weekly #leetcode solutions in #csharp! Drop your questions or alternative approaches in the comments below. Happy coding! 🚀 #codinginterview #algorithms #programming